UMEM Educational Pearls

Pressure Regulated Volume Control (PRVC)

• PRVC is a mode of mechanical ventilation that combines both volume and pressure control modes
• The main advantage to PRVC is that the tidal volume / minute ventilation is guaranteed while controlling airway pressures, thereby reducing the risk of ventilator induced lung injury
• In PRVC, the ventilator delivers a pressure-controlled breath, but tidal volume is the key setting
• The ventilator will automatically adjust inspiratory pressures until the desired TV is achieved
• When using PRVC you need to set: target TV, RR, peak pressure alarm, inspiratory time, FiO2, and PEEP

Currently Approved LMWHs for the Treatment of Acute PE:

• Enoxaparin-1 mg/kg every 12 hours subcut
• Tinzaparin 175 Units/kg once daily subcut
• The pentasaccharide: Fondaparinux- at a dose of 5 mg for body weight <50 kg, 7.5 mg for 50-100 kg, and 10 mg for >100 kg, once daily

Make sure to monitor platelet counts regardless of agent chosen.

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"The most common EKG abnormalities are non-specific ST-T wave changes, followed by RBBB. A normal EKG does not exclude the possibility of cardiac injury, although some investigators report a negative predictive value of up to 80-90%."

[El-Chami MF, Nicholson W, Helmy T. Blunt cardiac trauma. J Emerg Med 2008;35:127-133.]

Placing a foley catheter in a patient with BPH or acute urinary retention can be very difficult at times.  Here are some tips to increase your chance of a successful placement.

1. Use a Uroject lidocaine gel syringe to help anesthesize the urethra and lubricate the tract.  The lidocaine gel should be slowly expressed (injected) into the urethral meatus.  This helps to provide lubrication further down the urethra, as opposed to just wiping the catheter tip in the lubricant.
2. When using a Coude catheter, ensure that the curved tip points upward.
3. Apply gentle continuous pressure to help open the prostrate spincter.  This will be more successful than trying to ram it through which can increase spincter contracture.
4. Do not inflate the balloon until you have confirmed placement with urine return.
5. Don't forget the ultrasound.  You can calculate urinary volume (post void residual) prior to catheter placement and confirm placement with ultrasound.

If all else fails, a suprapubic catheter may need to be placed.  For a great review on evaluation and treatment please see Drs. Vilke, Ufberg, Harrigan, and Chan's article in the August edition of Journal of Emergnecy Medicine entitled Evaluation and treatment of acute urinary retention.

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Alcohol-Drug Interactions

• There are a number of medications that produce the disulfiram-like reaction when ingested with alcohol.
• The disulfiram reaction is a very uncomfortable reaction characterized by severe flushing, and may be accompanied by tachycardia and hypotension.
• Although we always think of metronidazole, there have been well described cases of bactrim causing this reaction.
• Tinidazole, a new antiprotozoal used in the treatment of trichomonas, causes this as well.
• Patients should be advised to avoid alcohol for 24 hours after metronidazole, and 72 hours after bactrim and tinidazole.

Other common medications that produce this reaction:

1. Sulfonylureas: chlorpropamide, tolbutamide, glyburide

2. Cardiovascular medications: Isosorbide dinitrate, nitroglycerin

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• About 2% of the adult population have an asymptomatic cerebral aneurysm.

• Unruptured aneurysms can cause symptoms such as headache, visual acuity loss, cranial neuropathies (particularly thrid nerve palsy), pyramidal tract dysfunction, and facial pain; these are thought to be due to mass effect on the aneurysm.

• 20 to 30% of people with a cerebral aneurysm, have multiple aneurysms; Don't miss co-existing aneurysms on CTA or MRI. 

• The majority of intracranial aneurysms are located in the anterior circulation, most commonly in the Circle of Willis.

• When localizing aneurysm on CTA and MRI, common sites include: 

              ---  junction of the anterior communicating artery (ACOM) with the anterior cerebral artery (ACA)

              ---  junction of the posterior communicating artery (PCOM) with the internal carotid artery (ICA)

              ---  bifurcation of the middle cerebral artery (MCA)

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Post-intubation deterioration?  Remember DOPE

• The pneumonic DOPE can help you remember the most common causes of post-intubation hypoxia or deterioration
• Displacement: check the endotracheal tube for displacement (right mainstem) or dislodgement
• Obstruction: check the ETT for obstruction (mucous plug, kink in ventilator tubing)
• Pneumothorax - get an xray
• Equipment failure(unusual): disconnect patient from the ventilator and bag manually   

 Necrotizing Fasciitis Pearl

A few things to remember about treating necrotizing soft tissue infections:

• Often polymicrobial and most of the time we in the ED won't have a microbial diagnosis
• If due to strep, patient may benefit from the addition of Clindamycin. Streptococcal species may stop multiplying in a wound/cellulitis and continue to produce large amounts of tissue toxin. In this case, many antibiotics (like the ubiquitous Zosyn-which works on dividing bacteria) may not work well. Clindamycin will actually affect toxin binding. The phenomenon of Strep species  dividing but continuing to produce toxin is referred to as the Eagle affect. 

So, when shot-gunning the antibiotics in a patient with a really bad soft tissue infection (not the run of the mill cellulitis) consider adding Clindamycin to the regimen. 

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Hemorrhagic and ischemic strokes are well-known to produce ECG changes that resemble cardiac ischemia. Large T-wave inversions are the most classic findings, but ST changes, prolonged QT interval, tachydysrhythmias, bradydysrhythmias, and AV blocks have also been described.

The exact cause of these changes is uncertain. One theory is that the strokes can produce catecholamine surges which cause the changes; another theory is that intracranial events produce a vagal response that causes ECG changes. Regardless of the reason, one should always keep stroke in the differential diagnosis for patients with ischemic-appearing ECG changes, especially when the patient has an altered mental status or neurologic deficit.

When examining a knee for a meniscal injury the commonly described tests are the McMurray Test and Apley Test.  However, these tests have sensitivities of 48-68% and 41% respectfully, and specificities of 86-94% and 86-93% respectfully.  Depending on whether you are looking at the medical or lateral meniscus.

The Tessaly Test that was first described in 2005 can be performed with knee in either 5 or 20 degrees of flexion and has a senstivity of 89-92% and specificity of 96-97% when performed in 20 degrees flexion.  The test also tends to be easier to perform.

To perform the test:

1. Stand on affected leg only with the other leg held up in the air.  The examiner holds hands for balance.
2. Flex knee to be test to 20 degrees, while the other leg is held in the air
3. Internally and Externally Rotate Knee
4. Positive test is pain at medial or lateral joint line with possible locking/catching sensation

Essentially you and your patient will look like you are doing the twist as they rotate their knee with you holding their hands.

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Sever's Disease

• Sever's disease is a painful inflammation of the calcaneal apophysis made worse with activity.
• It is thought to be caused by repetitive trauma to the weaker structure of the apophysis, induced by the pull of the Achilles tendon on its insertion.
• It occurs most frequently in active 10- to 12-year-old boys.
• The pain can limit performance and participation, and if left untreated, the pain can significantly limit even simple activities of daily life.
• Xrays are useful in ruling out other causes of heel pain like fracture or rare tumor but are not diagnostic or prognostic. 
• Treatment consist of rest, nsaids, wearing a half-inch inner-shoe heel lift (at all times during ambulation), a monitored stretching program, and presport and postsport icing. (rarely casting)
• Sever disease is a self-limited condition and will resolve after the growth plate fuses.

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• Tramadol (Ultram) is an uncontrolled substance in the opiod family that binds mu receptors and is indicated for moderate to moderately severe pain.

• Tramadol lowers seizure threshold to < 1/100,000, likely related to its inhibition of neuronal re-uptake of serotonin and norepinephrine in the CNS.

• Concurrent use with SSRI's, TCA's, MAOI's, neuroleptics, other opiods, naloxone (when given for tramadol overdose) and alcohol exacerbates the risk of seizure onset.

• Tramadol-related seizure is independent of dose (i.e. can occur at starting dose of 25 mg), although brisk titration up to maintenance doses does increase seizure risk.
•  
•  To avoid triggering a seizure, tramadol should not be used in patients with the following conditions:

             --  seizure disorder

             --  alcohol withdrawal

             --  alcoholism

             --  drug withdrawal

             --  CNS infections

             --  metabolic disorder

             --  head trauma

The Importance of Plateau Pressure

• Alveolar overdistention is a precursor to the development of acute lung injury (ALI)
• Plateau pressure is a measurement of alveolar overdistention, and is the pressure equilibration between the airways and the alveoli
• Plateau pressure is measured by using an inspiratory hold (for at least 3 seconds) at the end of inspiration
• Based on available data, you want to maintain the plateau pressure < 30 cm H₂O
• Remember that patients should be heavily sedated to obtain this measurement - any patient-ventilator asynchrony may provide inaccurate information

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Causes of an Elevated D-Dimer 

Don't forget the multiple causes of an elevated d-dimer:

• PE/DVT
• Sepsis/infection
• Malignancy 
• Renal disease
• Pregnancy
• MI
• Stroke

**See attached PDF-Differential Diagnosis of Elevated D-Dimer

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Attachments

0807301959_Causes_of_Elevated_D-Dimer.pdf (43 Kb)

There are many causes of rightward axis on electrocardiography: RVH, COPD, acute (e.g. PE) or chronic (e.g. COPD, cor pulmonale) pulmonary hyptertension, sodium channel blocking drug toxicity (e.g. TCAs), ventricular tachycardia, hyperkalemia, dextrocardia, left posterior fascicular block, prior lateral MI, and of course misplaced leads.

In emergency medicine, however, the causes of acute/NEW rightward axis constitutes a smaller list. Perhaps the two most important causes of acute/new rightward axis in emergency medicine that should be remembered are PE and sodium channel blocker toxicity. In both of these conditions, the rightward axis may be the only obvious finding on the ECG.

The takeaway point is this: when you see new righward axis (compared to an old ECG) and you see nothing else "jumping out" at you, consider PE and consider sodium channel blocker toxicity.

Most people are now using Ultrasound to aid in cannulation of the femoral and internal jugular veins, but if you find yourself without the ultrasound machine you can increase your chance of successful cannulation of the femoral vein by positioning the leg properly.

Werner et al looked at the common femoral veins of 25 healthy volunteers and noted that the femoral vein was accessable more often when the hip was abducted and external rotated.  This simple position change increased the mean diameter of the vein, and prevented the vein from being directly posterior to the artery.

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Pyloric Stenosis

• The cause of the hypertrophied pylorus muscle is unknown, but it is usually not present at birth.  Mean onset of symptoms is 2-3 weeks of life, but range can be birth to 5 months with a 4:1 male to female occurrence.
• Clasic presentation is projectile, nonbilious vomiting of last feed which may be immediate or hours later.
• Pyloric Stenosis is the most common reason for abdominal surgery in the first 6 months of life.
• Textbook lab abnormality is a Hypochloremic hypokalemic metabolic alkalosis but this is a later finding and can not be used to rule out the diagnosis.
• Ultrasonography has become the standard imaging technique for diagnosis. It is reliable, highly sensitive, highly specific, and easily performed.
• Muscle wall thickness 3 mm or greater and pyloric channel length 14 mm or greater are considered abnormal in infants younger than 30 days. 
• DDX includes :  Normal Regurgitation (all babies do it!!!), GERD, Milk Intorerance, Obstruction (antral webs, volvulus,intussusception)

• Elemental Mercury is found in manometers, some mercury switches and thermometers.
• Elemental Mercury is also in the CFLs (Compact Fluoroscent Lightbulbs) that are popular now due to rising energy cost (approx 4 mg)
• Organic mercury found in seafood is only toxic in high consistent doses - though has been catastrophic. See attached picture which was the award winning Time magazine cover of the year showing a mother holding her child who had congenital disfigurement due to mercury being dumped into Minamata Bay
• Elemental Mercury is mostly a neurotoxin causing personality changes, nervousness, shyness and depression.
• Acrodynia is pain and pink discoloration of hands and feet due to mercury poisoning in children.

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• Don't forget to check for distal lower extremity neurologic deficit after knee injury, particularly when there is a direct blow to the popliteal fossa.
• The common peroneal and tibial nerves exit from the lateral and middle sections of the popliteal fossa, respectively.
• The common peroneal nerve wraps laterally around the fibula (where it's palpable), primarily supplying the lateral portions of the lower leg and foot.
• The tibial nerve primarily supplies the muscles of the posterior compartment of the lower leg (i.e. gastrocnemius, soleus, popliteus).
• Both the common peroneal and tibial nerve fibres branch into the sural nerve, which supplies the lateral foot.
• Common peroneal also splits into deep and superficial branches which supply the muscles of the anterior lower leg compartment and lateral lower leg compartment, respectively.  The deep branch also provides cutaneous innervation of the cleft between the great and second toes.

--  IN SUMMARY:

• Neurologic deficit of the posterior lower leg muscles likely = tibial nerve injury.
• Neurologic deficit of the anterior and lateral lower leg muscles likely =  peroneal nerve injury.
• Decreased sensation in the web space between the great and 2nd toes likely = (deep) peroneal nerve injury.
• Decreased sensation over the lateral dorsum of the foot likely = sural nerve injury.

*** Speaking of such deficits by naming the affected nerve distribution is particularly helpful when consulting orthopedists, neurologists, etc.

Mechanical Ventilation in Asthma

• Approximately 25,000 asthmatics are intubated each year
• Mismanaged mechanical ventilation in asthma carries significant morbidity and mortality
• One of the primary goals of ventilating the asthmatic is to allow for lung deflation
• The most effective way to allow for lung deflation, and reduce hyperinflation, is to reduce minute ventilation (TV x RR)
• Initial tidal volume settings should be 6 ml/kg of predicted body weight; if plateau pressures are > 30 cm H₂O tidal volume should be decreased to 4 - 5 ml/kg
• Reduced respiratory rates will also allow longer exhalation times; initial recommended rates are 6 - 8 breaths per minute
• If plateau pressures are still high despite lowering tidal volume and respiratory rate, you can then shorten the inspiratory time to allow for longer exhalation

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